1. Technical Field of the Invention
The present invention relates to engine control apparatuses for vehicles and, more particularly, to an engine control apparatus and a related engine control method for controlling autostart (automatic startup) of an engine of a vehicle.
2. Description of the Related Art
In the related art, attempts have heretofore been made to provide engine control apparatuses for controlling startups of multi-cylinder engines installed on vehicles as disclosed in, for instance, Japanese Patent Application Publication No. 2003-254147 (Patent Publication 1) and Japanese Patent Application Publication No. 2003-49696 (Patent Publication 2).
Each of these multi-cylinder engines generally includes a crank sensor associated with a crankshaft to output a crank signal indicative of a rotational speed of the crankshaft and a cam sensor associated with a camshaft to output a cam signal indicative of a rotational speed of the camshaft. The engine control apparatus executes cylinder discrimination in response to the crank signal and the cam signal in combination to provide a cylinder discriminating result, based on which fuel injection and ignition are performed for each cylinder thereby causing the engine to operation. As used herein, the term “cylinder discrimination” refers to a phase wherein a rotary position of the crankshaft for one cycle (720° CA) of the engine is specified.
Further, a failure tends to occur in either the crank signal or the cam signal with no variation in signal level due to the disconnection of a sensor signal line or short-circuiting to a specified voltage potential. Under such occasion, cylinder discrimination is performed using a normal one of the crank signal and the cam signal to render the engine operative in technology disclosed in, for instance, Patent Publication 1.
Meanwhile, in recent years, the engine control apparatus of such a kind usually includes, for instance, a push-button type starter switch and is operative to authenticate a correct user of a vehicle. The authentication results in success when the push-button type starter switch is turned and a communication is established with a portable device carried by the user of the vehicle. Thus, the authentication means judgment made that the user is a right user.
An attempt has heretofore been undertaken to provide an autostart (automatic start) control device. Autostart control is performed upon the establishment of a startup initiating condition in receipt of the relevant authentication result. This automatically drives a starter motor to crank up the engine until judgment is made that the engine enters a running state (in complete combustion) as disclosed in, for instance, Japanese Patent Application Publication No. 2002-221132 (Patent Publication 3).
With a system carrying out autostart control of such a kind, in comparison to a manual type startup system wherein a starter motor is driven for a time period in which a user turns on a starter switch, the user has no need to continue the operation for startup of the engine until the engine reaches complete combustion. This results in an advantageous effect of enabling the improving productivity of the vehicle and no probability of driving the starter motor in an unwanted occasion such as the running of the engine.
Further, the engine control apparatus, performing the autostart control of this kind, is configured to drive the starter motor for a driving duration time provided with a limit time (drive enabling time for starter motor) (see, for instance, Patent Publication 3). That is, with the driving duration time reaching the limit time, the drive of the starter motor is interrupted due to a limiting function resulting from the limit time even if the engine does not enter the running state. This prevents the starter motor from being unnecessarily and continuously driven due to some failure in input conditions. In addition, this prevents the occurrence of battery dead or deterioration in battery due to the starter motor being driven for an extended period of time.
Meanwhile, under a situation where a failure occurs in either the crank signal or the cam signal and the cylinder discrimination is performed using only a normal signal, the engine control apparatus has less information for cylinder discrimination than that in which all the signals are normal. Therefore, this results in a long maximum time from timing at which the cranking of the engine begins, due to the starter motor being driven, to timing at which the cylinder discrimination is completed. Thus, when an attempt is made to start up the engine under a circumstance where some of the crank signal and the cam signal is not normally input, the maximum time for the starter motor to begin in operation to cause the engine to enter the running state becomes longer than that occurring in a normal mode.
Therefore, with the engine control apparatus performing the autostart control, if a failure occurs in some of the crank signal and the cam signal, the driving duration time of the starter motor reaches the limit time before the engine enters the running state after the motor has begun to be driven. When this takes place, the driving of the starter motor is interrupted, causing a probability with a difficulty of starting up the engine. Especially, under extremely cold environments, a drop occurs in battery voltage and a viscosity of lubricating oil increases. This causes a further increase to occur in time for the starter motor to begin in operation to complete the cylinder discrimination, resulting in a further increase in a probability for the startup of the engine to be disabled.